A potentially advantageous vehicular blind-zone detection system utilizes two or more passive IR sensors spaced along at least the driver side of the vehicle. The sensors are aimed at a lane adjacent the vehicle and respond to the temperature of objects (i.e., radiant energy or infrared radiation) in the respective coverage areas. As the vehicle is driven, the trailing sensor will respond to the same objects that the leading sensor responded to moments earlier; that is, the leading and trailing sensors will be responsive to the same stationary target area. The sensor outputs are therefore very similar when the adjacent lane is empty, but differ significantly when an object entering the blind-zone is registered by just one of the sensors—the trailing sensor, in the case of an over-taking vehicle. In operation, the sensor outputs can be monitored as the vehicle is being driven and used to produce a driver warning if lane changing is attempted or signaled when an object has been detected in the adjacent lane. Such a system is described, for example, in the Patent Publication No. 2002/0126002 A1, incorporated by reference herein.
As described in the aforementioned patent publication, the sensors must be aligned very carefully to ensure that they respond to the same stationary target area such as the vehicle blind-zone. When the sensors are properly aligned, there is a known and fixed separation distance between the coverage areas of the leading and trailing sensors so that the time delay between outputs produced by the leading and trailing sensors may be accurately determined based on the known separation distance and the vehicle speed. Although the vehicle speed can be measured very accurately using wheel speeds for example, proper alignment of the passive IR sensors cannot be easily verified, and the alignment of a given sensor could change for a variety of reasons depending on how it is mounted and whether the vehicle sustains even minor damage from a collision, for example.